1. Field of the Invention
This invention pertains to the bag making art and more particularly relates to a multipurpose sealing mechanism capable of making a plurality of different sizes, types, and styles of bags and/or sheets with a minimum of changeover time.
2. Description of Prior Art
In the thermosealing or thermoplastic bag making industry, bag producers are frequently required to make batches of bags in accordance with specific customer demands; which demands may require bags which vary considerably in size, shape, thickness, and types. Thus, prior art bag machines were made with changeover kits so that they could operate as either side weld machines, or bottom weld machines open end first or closed end first. This general type of machine could also be used to make sheets from web material provided the proper kit was installed on the machine.
U.S. Pat. No. 3,663,338 which issued on May 16, 1972 to Robert J. Wech illustrates a side weld machine. The side weld machine makes bags from a thermoplastic web which is foled longitudinally and accordingly is termed a J-fold. The machine intermittently passes a web between a heated reciprocating hot knife and a seal roller. Each stroke of the hot knife against the web both severs the web and heat seals both sides of the cut. This type of machine may also be used to form sheets of thermoplastic material from a web of the material.
Lotto U.S. Pat. No. 3,813,998 which issued on June 4, 1974 disclosed a bag machine that uses tubular web material and has many components identical to the Wech machine but is provided with a bottom weld, closed end first kit. This kit requires; that the Wech type seal bar be replaced by an upper seal bar and knife assembly with the knife disposed downstream of the seal bar, that the Wech roller be replaced by a stationary seal pad, that draw rolls of the machine be retimed to reverse the film thus stripping the film from the seal pad prior to advancing the web for another bag, and that a special film tensioning pick-off mechanism disposed downstream of the hot knife be provided to tension the film during the cutting operation to provide a better cut and prevent welding the open end of the bag closed.
A third type of bag machine, known as a bottom weld, open end first machine, is similar to the Lotto machine except that the change-over kit requires a sealing and severing head that places the hot knife upstream of the seal bars, does not require retiming of the draw rolls as compared to the Wech machine mentioned above, and does not require a special film tensioning pick-off mechanism as in the Lotto machine above.
Wech U.S. Pat. No. 3,779,838 which issued on Dec. 18, 1973 illustrates a bottom weld, closed end first machine which utilizes elongated heat sealing bars that are connected to associated rigid beams by a plurality of support bars rigidly attached to the beams. The support bars are secured to elongated heat sealing bars by resilient clamps thereby minimizing the problem of unequal sealing pressures being applied to the sealing bars due to uneven heat expansion of the bars.